Continuous casting plants, single line, known in the state of the art for the production of long rolled products have considerable limitations in that, for reasons intrinsically connected to operating constraints and performance of the components, their productivity does not generally exceed 25-40 ton/h. Consequently, in order to obtain higher productivity it is necessary to increase the number of casting lines connected to the same rolling line, which can be up to 8 lines or more. This entails, among other things, the need to translate the billets or blooms exiting from the various casting lines on a single entrance point of the heating furnace, with the consequent losses of temperature in the transfers.
The consequence of this is the considerable quantity of energy needed to feed the heating furnace, which has to restore the temperature lost and bring it from the entrance value, comprised between 650° C. and 750° C., to the value suitable for rolling, which is equal to about 1100° C.
Moreover, the need to transfer the segments of billets or blooms from the various casting lines to the point where they are introduced into the furnace, imposes limitations on the length and therefore the weight: the length of the billets or blooms is comprised between 12 and 14 m, up to a maximum of 16 m, and the weight is on average equal to 2-3 tons.
These process necessities and limitations are the main cause of an increase in energy required for heating the billets or blooms, and of a worsening of the full capacity, due both to the large-sized tundishes that are needed to serve several casting lines and also to the large number of billets or blooms to be processed given the same number of tons/hour to be produced, with consequent high number of crops, heads entering in the stands of the mill and sub-lengths with non-commercial sizes.
One purpose of the present invention is therefore to achieve a casting and continuous rolling process in semi-endless mode (that is, starting from segments of cast products sheared to size) for long products, and perfect a relative production plant which, using only one casting line, allows to increase productivity compared to similar plants in the state of the art.
Another purpose of the present invention is to exploit to the utmost the enthalpy possessed by the original liquid steel along all the production line, reducing temperature losses in the time between shearing the cast product to size and sending it to the rolling step, so as to obtain a considerable saving of energy and a reduction in the running costs compared to conventional processes.
A further purpose of the present invention is to deal with the stoppages of the rolling mill without having to interrupt the casting and therefore without loss of production and without penalizing the steel plant upstream.
Another purpose of the invention is to reduce to a minimum or eliminate the scrap material in emergency situations or during programmed stoppages and so completely recover the product which in these situations is temporarily accumulated in an intermediate point along the production line.
Further purposes of the invention are:
to reduce investment costs thanks to the reduction in the number of casting lines given the same production;
to guarantee a higher yield, equal to the ratio between weight of the finished product and weight of the liquid steel to produce a ton,
to reduce the risks of cobbles during the rolling thanks to the reduction in the number of heads entering in the stands;
to obtain a greater stability of the rolling mill and a better dimensional quality of the finished product;
to bring the performance of a semi-endless process much closer to that of an endless process, that is, without solution of continuity between the continuous casting machine and the rolling unit;
to guarantee the possibility of changes in production in dimension and type without stopping the continuous casting, obtaining a higher plant utilization factor.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.